Radio transmission systems of the prior art include radio transmission systems of the CDMA (Code Division Multiple Access)/TDD (Time Division Duplex) method that suppress the transmission power control error to a low level at mobile stations when diversity reception is performed by means of a plurality of antennas at a base station (For example, refer to Patent Document 1).
Alternatively, in OFDM (Orthogonal Frequency Division Multiplexing)—CDMA communication, there are transmitter-receivers that reduce the difference in amplitudes between subcarriers and maintain orthogonality between spreading codes to improve the transmission efficiency in a multi-path environment (for example, refer to Patent Document 2).
As another example, there are also communication terminal devices of the OFDM-CDMA method that compensate for residual phase errors (for example, refer to Patent Document 3).
In addition, communication devices of the OFDM-CDMA method also exist that prevent deterioration of the error rate characteristic of a demodulated signal without impairing transmission efficiency (for example, refer to Patent Document 4).
Multicarrier transmission devices of the multicarrier CDMA method also exist that neither require a broad frequency band nor cause high peaks in the signal waveform (for example, refer to Patent Document 5).
Still further, there are also OFDM communication devices that arrange information signals that have undergone direct sequence spreading in DS subcarriers to improve the transmission efficiency while suppressing the error rate characteristic of information signals (for example, refer to Patent Document 6).
Cellular spread-spectrum communication systems also exist in which each terminal device can communicate with a base station at a high S/N and that can increase the number of simultaneous communications in each cell (for example, refer to Patent Document 7).
OFDM-CDMA radio communication devices also exist that can prevent both increase in peak power and deterioration of communication quality (for example, refer to Patent Document 8).
In one method of estimating noise and interference power in a radio transmission device that employs CDMA, noise and interference power are estimated by despreading the received signal by means of a spreading code that is not used in spreading the pilot signal. This explanation takes a case in which spreading codes that are spread on the time axis at spreading rate 4 as shown in FIG. 1. The four codes:    Code 1: (1, 1, 1, 1)    Code 2: (1, 1, −1, −1)    Code 3: (1, −1, 1, −1)    Code 4: (1, −1, −1, 1)are taken as spreading codes. The three codes Code 1, Code 2, and Code 3 are used in the spreading of the pilot signal. If the channel impulse response of the chip spacing is h1, h2, h3, and h4; and the noise and interference components that correspond in time to these values are NI1, NI2, NI3, and NI4, the received signal r is expressed by the following formula:r=(h1+h2+h3+h4)+(h1+h2−h3−h4)+(h1−h2+h3−h4)+NI1+NI2+NI3+NI4 =(3h1+h2+h3−h4)+NI1+NI2+NI3+NI4 
Despreading signal d, in which this value is spread by Code 4 that was not used in the spreading of the pilot signal, is:d=(3h1−h2−h3−h4)+NI1−NI2−NI3+NI4 
In this case, if:h1≈h2≈h3≈h4  [Formula 1]is true, then:d≈NI1−NI2−NI3+NI4  [Formula 2]and, since only the noise and interference components remain, the noise and interference power can be estimated by finding the average value of the square of this value. However, when channel fluctuation on the time axis is great,h1≈h2≈h3≈h4  [Formula 3]is not realized, and the accuracy of the estimation is thus degraded.
In CDMA, spreading is implemented only on the time axis, but radio transmission methods in which two-dimensional code spreading is carried out on the time axis and frequency axis include MC-2D-CDMA (for example, refer to Non-patent Document 1). In MC-2D-CDMA, two-dimensional code spreading is sometimes used for the pilot signal. It is here assumed that a pilot signal is used that is spread two chips on the time axis and two chips on the frequency axis at a spreading rate 4 as shown in FIG. 2. As with the example of CDMA, a case is here considered in which the three codes Code 1, Code 2, and Code 3 are used to spread the pilot signal, and noise and interference power are estimated by despreading the received signal by Code 4. The channel impulse response values that correspond to C0, C1, C2, and C3 of FIG. 2 are h11, h21, h12, and h22, respectively; and the noise and interference components are NI11, NI21, NI12, and NI22. As a result of the convolution operation of received signal r and code 4 at this time, despreading signal d is:
                    d        =                ⁢                                            (                                                3                  ⁢                                      h                                                                                                              ⁢                      11                                                                      +                                  NI                                                                                                    ⁢                    11                                                              )                        ×            1                    +                                    (                                                h                                                                                                    ⁢                    21                                                  +                                  NI                                                                                                    ⁢                    21                                                              )                        ×                          (                              -                1                            )                                +                                                ⁢                                            (                                                h                                                                                                    ⁢                    12                                                  +                                  NI                                                                                                    ⁢                    12                                                              )                        ×                          (                              -                1                            )                                +                                    (                                                -                                      h                                                                                                              ⁢                      22                                                                      +                                  NI                                                                                                    ⁢                    22                                                              )                        ×            1                                                  =                ⁢                              (                                          3                ⁢                                  h                                                                                                    ⁢                    11                                                              -                              h                                                                                          ⁢                  21                                            -                              h                                                                                          ⁢                  12                                            -                              h                                                                                          ⁢                  22                                                      )                    +                      NI                                                                      ⁢              11                                -                      NI                                                                      ⁢              21                                -                      NI                                                                      ⁢              12                                +                      NI                                                                      ⁢              22                                          
Here, if:h11≈h21≈h12≈h22  [Formula 4]then:d≈NI11−NI21−NI12+NI22  [Formula 5]and, because only the noise and interference components remain, the noise and interference power can be estimated by finding the average value of the square of this value.    Patent Document 1:            Japanese Patent Laid-Open Publication No. 2000-91986            Patent Document 2:            Japanese Patent Laid-Open Publication No. 2001-24618            Patent Document 3:            Japanese Patent Laid-Open Publication No. 2001-28557            Patent Document 4:            Japanese Patent Laid-Open Publication No. 2001-144724            Patent Document 5:            Japanese Patent Laid-Open Publication No. 2001-168837            Patent Document 6:            Japanese Patent Laid-Open Publication No. 2001-203664            Patent Document 7:            Japanese Patent Laid-Open Publication No. 2002-198902            Patent Document 8:            Japanese Patent Laid-Open Publication No. 2002-271296            Non-Patent Document 1:            The Proceedings of PIMRC 1999, pp. 498-502.        
However, the problem occurs that, when the noise and interference power estimation method that is conventionally used in the above-described CDMA is applied without alteration to a pilot signal that is subjected to two-dimensional spreading as described above, the estimation accuracy deteriorates dramatically if the channel fluctuation on both the frequency axis and the time axis is not sufficiently low. For example, even when fluctuation on the time axis is almost absent, i.e., even when:h11≈h12 and h21≈h22  [Formula 6]then d is:d≈2h11−2h21+NI11−NI21−NI12+NI22  [Formula 7]and if the fluctuation on the frequency axis is great, i.e. if:h11≈h21  [Formula 8]is not realized, then a signal component remains and the estimation accuracy deteriorates. Even if there is no fluctuation on the frequency axis, i.e., even if:h11≈h21 and h12≈h22  [Formula 9]d is:d≈2h11−2h12+NI11−NI21−NI12+NI22  [Formula 10]and if the fluctuation on the time axis is great, i.e., if:h11≈h12  [Formula 11]is not realized, then a signal component remains and the estimation accuracy deteriorates.